A couple of days ago, Lumpy44 made a post asking who used watermarks. It reminded me of this hands on review I came across on Electronista of a program called iWatermark+. I've been meaning to check it out, but just haven't gotten around to it. Perhaps somebody might find it useful.

...create your own watermark from scratch. These can be signatures, they can be graphics like your company logo, they can be text. They can even be invisible metadata ones that you can use to show a photo is yours, even though it doesn't have a distracting watermark graphic slapped across it.